Why not give the auditor the data and Client NFR copies of Invoices and GridView (or all of Adagio for that matter)? Or, install the client NFR of ePrint and have a clerk sit and print the "Print" button and generate the requisite PDF's one by one?

In answer to your question, there's rarely a "hard and fast" limit in software. Changing the behaviour of something as fundamental as the Grid in Adagio requires a TON of QA, and those resources have been in short supply.